There are, however, good reasons to limit the government benefits associated with marriage.***Why?

First, I should say I don't think there should be any government benefits linked to marriage per se.

To answer your question though, a reason to limit such benefits is necessary to discourage fraudulent marriage for the purpose of acquiring benefits. Can that happen in monogamous marriage? Sure, but the consequences are limited. Maybe there's another solution to that problem. Haven't given it a great deal of thought.

But generally speaking, and again, how many wives or husbands someone has, and whether those relationships are hetero- or homosexual, really isn't anyone's business. Especially not the state's. If churches want to impose religious restrictions on sanctioning such marriages, that's their prerogative.